Part 13 (1/2)
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Bipinnate; on anterior surface of tibiotarsus deep to M. tibialis anticus; bounded laterally by M.
peroneus brevis; lateral edge usually slightly fused to proximal half of latter; medial surface fused to aponeurosis of M. peroneus longus.
ORIGIN.--The muscle arises fles.h.i.+ly from the lateral surface of the inner cnemial crest, from the rotular crest between the cnemial crests (deep to the attachment of M. tibialis anticus), from the basal (medial) half of the anterior surface of the outer cnemial crest, and from the anterior surface of the tibiotarsus (except the distal part) between the anteromedial and anterolateral intermuscular lines; proximal to the anterolateral intermuscular line, the origin usually extends almost to the lateral edge of the tibiotarsus.
INSERTION.--The ossified tendon extends along the mid-anterior surface of the distal part of the tibiotarsus deep to the tendon of M. tibialis anticus and pa.s.ses under the supratendinal bridge, becoming flexible and widening slightly as it crosses the anterior surface of the intratarsal joint; the tendon narrows again and pa.s.ses through a small but strong retinaculum on the anterior surface (medial to midline) of the proximal part of the tarsometatarsus; the retinaculum is immediately proximal and medial to the insertion of M. tibialis anticus. The tendon ossifies again as it pa.s.ses down the anterior surface of the tarsometatarsus and bifurcates near the midpoint of the latter; the lateral branch soon bifurcates again; of these three branches, which are ossified for some distance, the lateral one pa.s.ses onto the dorsal surface of digit IV, the middle one pa.s.ses onto the dorsolateral surface of digit III, and the medial one subdivides (at the level of the trochleae) into three branches--one pa.s.sing onto the dorsal surface of digit III and two pa.s.sing onto the dorsal surface of digit II. At the level of the metatarsophalangeal joints, all of these tendons are interconnected by strong sheets of connective tissue and it is often difficult exactly to delimit the tendons at this level. On the digits, tough connective tissue binds the tendons to the phalanges; this is most p.r.o.nounced at the interphalangeal joints. The tendons are distinct on the first phalanx of each digit, but are often poorly defined farther distally. On _digit IV_ the tendon subdivides into branches that attach to the proximal ends of the ungual, fourth, third, and (usually) second phalanges. On _digit III_ the lateralmost tendon bifurcates, with one branch attaching to the ungual phalanx and the other to the proximal end of the third phalanx; the medial tendon attaches to the proximal end of the second phalanx. On _digit II_ the originally medial tendon pa.s.ses underneath and then lateral to the other tendon and attaches to the ungual phalanx; the other tendon attaches to the proximal end of the second phalanx.
INNERVATION.--One or more branches of the peroneal nerve enter the lateral edge.
INDIVIDUAL VARIATION.--In four legs, the lateral branch of the trifurcated tendon is not ossified at all.
_T. cupido_
INDIVIDUAL VARIATION.--In a few cases, the muscle does not come in contact with M. peroneus brevis.
_P. p. jamesi_
DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The belly is shorter. The lateral branch of the tendon on the tarsometatarsus is not ossified (true also of some legs of _Tympanuchus_).
INDIVIDUAL VARIATION.--In several legs, the muscle also arises from the distal part of the posterior surface of the outer cnemial crest.
=_M. Peroneus Brevis_=, Figs. 14, 16, 17, 18, 19A
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Small; on lateral surface of distal part of tibiotarsus; mainly anterior to fibula; bounded posteriorly and laterally by M. flexor digitorum longus (fused with latter), anteriorly by M. tibialis anticus, and anteromedially by M. extensor digitorum longus (usually slightly fused to latter).
ORIGIN.--The muscle arises by fleshy and tendinous fibers from the medial and anterior surfaces of the fibula beginning a short distance below the distal end of the fibular crest and from the anterolateral surface of the tibiotarsus anterior to the fibula; the anteromedial edge attaches to the anterolateral intermuscular line.
INSERTION.--The short, slender, ossified tendon pa.s.ses along the anterolateral surface of the tibiotarsus and through a retinaculum immediately proximal and anteromedial to the retinaculum for the anterior branch of the tendon of M. peroneus longus; the tendon becomes flexible and widens as it pa.s.ses across the lateral surface of the intratarsal joint deep to the tendon of M. peroneus longus, turning posteriorly and attaching to the proximolateral corner of the hypotarsus.
INNERVATION.--The superficial peroneal branch of the peroneal nerve gives one or two twigs to the anterior surface of the proximal part.
INDIVIDUAL VARIATION.--None of significance.
_T. cupido_
INDIVIDUAL VARIATION.--In a few legs, the muscle does not come in contact with M. extensor digitorum longus.
_P. p. jamesi_
INDIVIDUAL VARIATION.--None of significance.
=_M. Extensor Hallucis Longus_=, Figs. 19E, 20N
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Slender and elongate; proximal part on anterior surface of tarsometatarsus medial to anterior metatarsal groove; near midlength of tarsometatarsus, muscle twisted onto medial surface of latter; divisible into two heads--proximal and distal; belly of proximal head (largest) ending at level of twisting onto medial surface of bone; short distal head beginning at this point deep to tendon of proximal head and soon joining latter tendon.